The invention relates generally to a color filter and more particularly to a color filter formed by electrochemical methods for a color image display device such as a liquid crystal panel. For example, a color filter described in U.S. patent application Ser. No. 07/344,636 filed Apr. 4, 1989 is formed by first dispersing an organic pigment in an aqueous micellar solution. The solution includes surfactant that has redox reactivity to form colloids. The solution is then electrolyzed to deposit the organic pigment on a transparent electrode that is formed on a transparent substrate.
When a liquid crystal panel is required to have high liquid crystal driving properties, it is undesirable to have a loss of applied voltage. The organic pigment formed on the driving electrode typically has a high resistance and leads to a loss of applied voltage. This diminishes the driving properties of the liquid crystal display device.
Conventional organic pigment films have other drawbacks. The organic pigment films are formed of fine particles and the adhesion between the particles and the substrate and among the particles is due to physical adsorption which is a weak force. Portions of the pigment film can peel off after film formation, during washing procedures such as those employing ultrasonic waves, when the panel is formed and during the rubbing treatment for orienting the liquid crystal material. If only an upper portion of the film peels off, the uneven film surface can lead to insufficient orientation of the liquid crystal material and non-uniform contrast.
The thickness of a pigment film is set to optimize the color tone. The thickness of the red, green and blue (for example) films can differ by about 0.5 .mu.m between the thickest and thinnest film. If these films are included in a panel that includes super twisted nematic (STN) type liquid crystal material, an uneven display having contrast fluctuations can occur because of the non-uniform (.+-.0.05 .mu.m) cell gaps. Accordingly, it is necessary to form each of the thin film color filters with the same thickness to have uniform liquid crystal cell gaps.
When a color filter is formed as described in U.S. patent application Ser. No. 07/344,636, the color pigment thin film will form wherever the electrode is in contact with the micellar solution. Accordingly, a pigment thin film will form on a sealing portion to which a reference electrode is adhered or to a portion of a driving IC that is connected during the panel forming procedure. The presence of pigment in these locations reduces the durability of the panel because there will be insufficient adhesion at the sealing portions of the panel and the IC can be inadequately connected.
To alleviate this problem, the pigment film can be wiped from the sealing portion and the IC connection portion. However, this takes additional steps and it can be difficult to completely remove the pigment film. As with the other drawbacks, this can lead to increased cost and a reduction in quality.
Accordingly, it is desirable to provide an improved method of forming a color filter and a color filter which do not have the shortcomings noted above.